Downloaded from genesdev.cshlp.org on October 5, 2021 - Published by Cold Spring Harbor Laboratory Press SPECIAL SECTION: REVIEW Nuclear PARPs and genome integrity Kameron Azarm and Susan Smith Department of Pathology, Kimmel Center for Biology and Medicine at the Skirball Institute, New York University School of Medicine, New York, New York 10016, USA Effective maintenance and stability of our genomes is es- et al. 2018). Here we focus on the four family members sential for normal cell division, tissue homeostasis, and that catalyze PARylation (PARP1 and PARP2 and tankyr- cellular and organismal fitness. The processes of chromo- ase 1 and tankyrase 2) and how they function in the nucle- some replication and segregation require continual sur- us to promote genome stability. We first compare and veillance to insure fidelity. Accurate and efficient repair contrast PARP versus tankyrase and discuss the role of of DNA damage preserves genome integrity, which if the poly(ADP-ribose) (PAR) modification. We provide an lost can lead to multiple diseases, including cancer. Poly overview of PARPs in DNA repair, highlighting recent (ADP-ribose) a dynamic and reversible posttranslational studies on their role during DNA replication and in phase modification and the enzymes that catalyze it (PARP1, separation. Finally, we focus on the role of tankyrases in PARP2, tankyrase 1, and tankyrase 2) function to main- telomere maintenance and chromosome resolution. tain genome stability through diverse mechanisms. Here we review the role of these enzymes and the modification in genome repair, replication, and resolution in human Compare and contrast: PARP1 and PARP2 versus cells. tankyrase 1 and tankyrase 2 Structure, mode of action, and function Structure PARP1, the founding member of the PARP Background: PARP1 and PARP2 and tankyrase 1 family, is the most well studied and known for its role and tankyrase 2 in DNA damage repair (DDR) (Martin-Hernandez et al. 2017; Ray Chaudhuri and Nussenzweig 2017). The Enzymes that catalyze PARylation primary structure of PARP1 comprises an N-terminal ADP-ribosylation (ADPr) is a posttranslational modifica- three-zinc-finger domain (Zn1, Zn2, and Zn3), an internal tion that regulates multiple cellular processes (Gupte BRCA C terminus (BRCT) domain followed by a Trp–Gly– et al. 2017). ADPr is catalyzed by the ADP-ribosyltransfer- Arg (WGR) domain, and a C-terminal catalytic domain ase (ART) superfamily of enzymes (Palazzo et al. 2017). comprised of a helical domain (HD) in close association The best-studied family of this group is the poly(ADP-ri- with the ART domain (Fig. 1A; Langelier et al. 2012, bose) polymerases (PARPs). The PARP family is com- 2018a). One of the earliest events in DNA repair is recruit- prised of 17 members that share an ART diphtheria ment of PARP1 to DNA. PARP1 binds to a range of DNA toxin-like (ARTD) domain and, hence, is also referred to structures like cruciforms (Brázda et al. 2011) and DNA as the ARTD family (Amé et al. 2004; Hottiger et al. damage structures, including nicked and gapped single- 2010). PARPs transfer a single or multiple ADP-ribose strand breaks (SSBs) and overhang and blunt-ended dou- unit(s) from nicotinamide adenine dinucleotide (NAD+) ble-strand breaks (DSBs) (Beck et al. 2014b). In the absence to protein acceptors. PARP family members that perform of genotoxic stress PARP1 is catalytically inactive. The + poly(ADP-ribosyl)ation (PARylation) include PARP1 and HD regulates catalytic activity by blocking NAD bind- PARP2, which synthesize long branched chains of up to ing. Upon detection of DNA damage, the Zn fingers and 200 units, and tankyrase 1 and 2, which synthesize shorter WGR domain organize around the DNA break, inducing unbranched chains of up to 20 units (de Murcia and an allosteric destabilization of the HD that enables + Menissier de Murcia 1994; D’Amours et al. 1999; Ripp- NAD to access the catalytic active site (Dawicki-McKen- mann et al. 2002; Vyas et al. 2014). The remaining mem- na et al. 2015; Langelier et al. 2018b). PARP2 and the bers of the PARP family are not as well studied, but closely related PARP3 [a mono(ADP-ribosyl) transferase] most catalyze mono(ADP-ribosyl)ation (MARylation) lack the Zn fingers and BRCT domain of PARP1, but share and have a range of functions throughout the cell (Lüscher © 2020 Azarm and Smith This article is distributed exclusively by Cold Spring Harbor Laboratory Press for the first six months after the full-issue [Keywords: PARP; tankyrase; genome integrity] publication date (see http://genesdev.cshlp.org/site/misc/terms.xhtml). Corresponding author: [email protected] After six months, it is available under a Creative Commons License (Attri- Article published online ahead of print. Article and publication date are bution-NonCommercial 4.0 International), as described at http://creative- online at http://www.genesdev.org/cgi/doi/10.1101/gad.334730.119. commons.org/licenses/by-nc/4.0/. GENES & DEVELOPMENT 34:285–301 Published by Cold Spring Harbor Laboratory Press; ISSN 0890-9369/20; www.genesdev.org 285 Downloaded from genesdev.cshlp.org on October 5, 2021 - Published by Cold Spring Harbor Laboratory Press Azarm and Smith A ankyrin repeat domain, and an N-terminal HPS (His, Pro, and Ser) domain of unknown function, unique to tankyr- ase 1 (Fig. 1C; Smith et al. 1998). The SAM domain of tankyrases can promote homo- and hetero-oligomeriza- B tion of tankyrase 1 and tankyrase 2; polymerization is re- quired for full catalytic activity (De Rycker and Price 2004; Mariotti et al. 2016; Riccio et al. 2016b; Fan et al. 2018). A distinguishing feature of tankyrases is their abil- ity to interact (through the ankyrin repeat domain) with a C broad range of binding partners (Fig. 1D). The ankyrin domain is organized into five ankyrin repeat clusters (ARCs), which serve as a basic unit for recognizing an eight amino acid segment (with a strict requirement for Arg at position 1 and Gly at position 6 [RxxxxG]) in its D binding partners (Sbodio and Chi 2002; Seimiya and Smith 2002; De Rycker et al. 2003; Guettler et al. 2011; Eise- mann et al. 2016). Four of the five ARCs (1, 2, 4, and 5) are each capable of recognizing a peptide motif. Proteomic and in silico screens have identified hundreds of potential tankyrase interacting proteins (Guettler et al. 2011; Bhardwaj et al. 2017; Li et al. 2017). Over 40 human tank- yrase-binding partners have been validated by coimmuno- Figure 1. Primary structure and mode of action for PARP1 and precipitation; they localize throughout the cell and most PARP2 and tankyrase 1 and tankyrase 2. (A) Schematic represen- contain a consensus peptide that (where it has been tested) tation of PARP1 and PARP2. (Zinc fingers) Zn1, Zn2, and Zn3; (BRCT) BRCA C terminus; (WGR) Trp–Gly–Arg domain; (HD) binds to both tankyrase 1 and tankyrase 2 (Fig. 2). This re- helical domain; (ARDT) ADP-ribosyltransferase. (B) PARP1 or view will focus on those partners that reside in the nucle- PARP2 is regulated through its catalytic activity. Inactive us and have been shown to influence genome stability. PARP1 binds to breaks and is activated to undergo autoPARyla- tion. PAR serves to recruit DNA repair proteins. (C) Schematic Mode of action Despite the fact that tankyrases and representation of tankyrase 1 and tankyrase 2. (HPS) His–Pro–Ser PARP1 and PARP2 share the ability to catalyze synthesis domain; (SAM) sterile α module; (ART) ADP-ribosyltransferase. of ADP-ribose polymers, tankyrases differ from PARP1 (D) Tankyrase 1 or tankyrase 2 is regulated through its selection and PARP2 in multiple ways. Tankyrases do not bind of binding partners. Constitutively active tankyrase binds to directly to DNA and they are not induced by DNA breaks RxxxxG-containing proteins and localizes throughout the cell to promote rapid synthesis of long PAR chains (Cook et al. for multiple functions. Tankyrase may (or may not) PARylate its partner. 2002). The tankyrase 1 and tankyrase 2 catalytic ART do- mains lack the regulatory HD found in PARPs 1 and 2, rendering them accessible to NAD+ binding. Analysis of a common WGR domain that interacts with DNA (albeit the PARylation status in cells shows tankyrase 1 to be with different substrate specificities) and regulates their constitutively autoPARylated with relatively short PAR catalytic activity in response to DNA damage (Langelier chains (Smith and de Lange 2000; Cook et al. 2002; Chang et al. 2014; Grundy et al. 2016; Obaji et al. 2016, 2018; Ric- et al. 2005). So far, there does not appear to be a mecha- cio et al. 2016a). nism for dramatic induction of tankyrase PARP activity Binding to breaks stimulates rapid and extensive syn- along the lines of the massive stimulation of PARP1 by thesis of PAR onto PARP1 itself (autoPARylation) (Satoh DNA damage. Studies suggest that SAM domain-mediat- and Lindahl 1992). The PAR then may prevent immediate ed polymerization can regulate tankyrase catalytic activi- inappropriate processing of the damage by blocking access ty (Mariotti et al. 2016; Riccio et al. 2016b; Fan et al. 2018), to nucleases (Caron et al. 2019) while simultaneously act- although how this would be regulated in vivo to stimulate ing as a recruitment platform for nucleases (Wang et al. or induce tankyrase-mediated PARylation remains to be 2019) and other proteins that bind PAR to repair the dam- determined. Another distinguishing feature between age (Fig. 1B). Excessive PARylation can induce release of PARP1 and PARP2 and tankyrases is that while PARP1 PARP1 from the DNA. The turnover of the PAR chains and PARP2 are predominantly nuclear, tankyrases (in ad- is also regulated rapidly through the glycohydrolase dition to their nuclear localization) are distributed PARG (Lin et al.